Some airports around the world still operate under the practice of atmospheric pressure at field elevation (QFE). At QFE airports, Automatic Terminal Information Service (ATIS) or a similar outputted system outputs a barometric pressure setting value. This value is one that when an aircraft is positioned on the ground at the airport the barometric altimeter reading in the aircraft will read zero regardless of the altitude of the airport. Therefore, as shown in FIG. 1, if an aircraft is flying to a QFE airport that is at the elevation of 1000 feet, the barometric altimeter indicates that the aircraft is 1000 feet lower than it actually is. This does not become a problem if the aircrew informs all systems within the aircraft that use barometric pressure that it is based on a QFE setting. However, if the aircrew fails to make sure the other aircraft systems understand that the barometric altimeter is based on QFE operation, then the other aircraft systems will produce false alerts. For example, as the aircraft is descending towards the airport, a Terrain Awareness System (TAWS) produces caution and warning alerts as the aircraft is on approach to the airport because the TAWS believes that the aircraft is 1000 feet closer than it actually is to the ground. Since the aircraft is actually flying 1000 feet higher, this alert is a nuisance alert. Because of the number of tasks performed on an approach to landing, the flight crew may be overloaded and not want to bother with figuring out the cause of the alert and thus just deactivate the TAWS. Deactivation of the TAWS leaves the aircraft vulnerable to controlled flight into terrain (CFIT).
Therefore, there exists a need to automatically detect the use of QFE operations to avoid nuisance alerts such as altitude monitor function alerts.